1. Field of the Invention
The present invention relates generally to sealing gaskets used for pipe joints in which a male spigot pipe section is installed within a mating female socket pipe section.
2. Description of the Prior Art
Pipes formed from thermoplastic materials including polyethylene and PVC are used in a variety of industries. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint. Previous attempts to stabilize the sealing ring within its mating groove included the provision of internal and external reinforcing rings or bands which provided additional rigidity for the resilient ring.
Attempts were also made to reinforce the pipe groove or adjacent pipe wall. One early attempt to ensure the integrity of pipe joints used under demanding conditions was to provide local reinforcement of the groove portion of the female socket end by means of a heavier wall thickness in this region of the pipe. In some cases, reinforcing sleeves were also utilized. Each of these solutions was less than ideal, in some cases failing to provide the needed joint integrity and often contributing to the complexity and expense of the manufacturing operation. Even in applications where pressure conditions are not as extreme, as in sewer pipe and irrigation pipe, it is desirable to properly position the gasket and insure its integrity.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the "Rieber Joint." The Rieber system employed a combined mold element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Rieber process, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belling end was simultaneously being formed. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
The Rieber system provided an integrally installed gasket which overcame many of the deficiencies of the prior art devices in maintaining the sealing ring in its proper position during installation and use. As the female socket end of the pipe cooled around the previously installed gasket, the elastomeric body of the gasket was compressed between a steel reinforcing ring and the groove formed in the socket end of the pipe. When the mating spigot was installed to make up a pipe joint, further compression of the gasket occurred in a radial direction along an internal compression region of the gasket.
Despite the advances offered by the Rieber process, the compression seal geometry presented problems in certain field applications. In some applications, particularly involving larger diameter pipe, the insertion force needed to install the male spigot end within the mating female socket end required a high insertion force which could, on some occasions, cause the gasket to be distorted or displaced. Also, with applications involving thin wall pipe such as irrigation pipe, the forces involved during manufacture using a Rieber type process could cause the pipe to stretch, thereby decreasing the wall thickness in the gasket region to unacceptable levels.
The present invention has, as one object, to provide a pipe gasket for use in such diverse systems as sewer pipe and irrigation pipe which offers the advantages of a Rieber style gasket while avoiding the previously mentioned problems encountered in the prior art.
Another object of the invention is to provide such a pipe gasket which provides a lower profile and consequent lower insertion force for the male, spigot end when entering the female, socket end to facilitate assembly of the pipe joint in the field.
Another object of the invention is to provide a sealing system of the above type in which a sealing gasket is installed within a groove provided within a female, socket end of a thermoplastic pipe in which the gasket is designed with a lower profile to facilitate belling operations in a Rieber type process involving thinner wall pipe to reduce stress on the pipe walls adjacent the sealing gasket groove to thereby prevent unacceptable stretching and thinning of the pipe wall.
Another object is to provide an improved gasket for use in such a sealing system in which the gasket is formed from a single, generally homogeneous composition, rather than having distinct regions of diverse materials such as varying durometer rubber regions or regions of plastic and rubber.
Another object of the invention is to provide a gasket with a low profile and lip type configuration which will allow assembly without a chamfer on the spigot end of the pipe.